An insulating holder for connecting a common rail of a fuel injection system for the direct injection of fuel to an internal combustion engine is discussed in U.S. Pat. No. 7,682,117 B2. Clamping elements are provided, which face each other, and are used as prestressing limiters and have a damping ring made of an elastomer assigned to them in each case. In the fastening, the axial prestressing excursion is limited via a gap between the clamping elements.
In the holder of U.S. Pat. No. 7,682,117 B2, it is therefore possible to use two annular elastomeric components in combination with two metal sleeves for the damping, while the prestressing is limited. The limitation is adjustable via the defined gap, in this instance. The gap is bridged during the screwing connection, and the annular elastomeric components are prestressed. The clamping force or the prestressing of the elastomeric components may be set via the axial stiffness and via the specified gap height. As soon as the metal sleeves reach a hard stop, the additional screw prestressing is no longer introduced into the elastomeric components but rather into the metal components. This protects the elastomeric components against overexpansion and against failure when the tightening torques are too high.
The functioning principle, from U.S. Pat. No. 7,682,117 B2, for separating prestressing and screw prestressing force has several disadvantages, however. Based on the concept, the elastomeric components see a large prestressing or preexpansion, in order to ensure the axially minimum clamping force. This already results in a substantial prestressing of the elastomeric components after assembly. Based on the separate part tolerances, particularly measurements of height, of the elastomeric components and the metal sleeves, in addition, tolerance-conditioned scattering of the preexpansion set in the elastomeric components. Above all, thin elastomeric components are very susceptible with respect to this tolerance chain, whereby design clearances are lost. The maximum boundary samples prestressed the most for tolerance-related reasons are especially at risk of tearing, whereas the corresponding minimum boundary samples result in a low clamping force with respect to the internal combustion engine.
It is just as little possible to use optionally resilient elastomeric components, since these result in higher, quasi static displacements of the fuel distributor and of the injection valve with regard to the initiation of operating forces which, in turn, would lead to increased wear of the seals of the injection valves. As a further disadvantage, the elastomer material is able to move at the boundary layers between the elastomeric components and the metal sleeves, tangentially to the rigid metal surface. This effect leads to heavy abrasion of the elastomer at the contact surfaces, and thus to a high risk of failure of the elastomeric components.